A process for the removal of sulfur dioxide from waste gases and recovery of the sulfur values as sulfuric acid is disclosed in U.S. Pat. No. 5,344,529. This patent describes a bipolar process in which an effluent vent or flue gas containing sulfur dioxide is scrubbed with an aqueous acid stream in an absorption column. The column contains an electrically conductive packing material that serves both as the gas-liquid contact surface and as the electrochemically active surface of a bipolar electrode. Thus, the sulfur dioxide is simultaneously absorbed in the acid and the dissolved sulfur dioxide is subjected to electrolysis. Byproduct sulfuric acid produced by the process is continually withdrawn from the system.
Electrical energy required for electrolysis in the bipolar process is supplied in the form of a direct current. This current, if obtained from a power grid, must first be stepped down to the necessary voltage and then rectified. A substantial investment is required in the electrical equipment to accomplish this task. Even if the process is used to scrub the flue gases from a power plant, the need for direct current is an additional cost.
Besides being concerned with the adjustment and regulation of the electrical power supply, the operator must face certain inherent inefficiencies in the bipolar process. The theoretical potential required for the electrolytic reaction is 0.2 volts. In practice, however, a minimum of 0.6 volts is needed before any reaction is obtained. This excess voltage, which is necessary, is attributed to electrode polarization caused by the irreversibility of the reactions.
The cost of electrical power consumed by the bipolar process is not inconsequential. As a result, any opportunity to reduce such cost is noteworthy. Even if the ideal case cannot be achieved, a significant improvement would greatly enhance the attractiveness of the process. Improved electrical efficiency would not only save expenses with regard to the direct power cost, but it also promises to increase the capacity of an installed scrubbing unit. Given the same electrode area, additional sulfur dioxide could be oxidized to sulfuric acid.
Therefore, it is an object of the present invention to provide a process which overcomes, or at least minimizes, the disadvantages of existing methods for removing sulfur dioxide from waste gases. It is an object to reduce electrical power consumption, to minimize the investment in electrical equipment, and to maximize the capacity of the process to remove sulfur dioxide.
These and other objects, features and advantages of the invention will become apparent from the following description and the accompanying drawings, FIGS. 1 and 2.